1. Field of the Invention
The present invention relates to a brake apparatus for a vehicle. In particular, the present invention relates to a brake apparatus for a vehicle provided with an actuator for carrying out antiskid control (ABS actuator).
2. Description of the Related Art
Antiskid control (ABS control) is for adjusting wheel braking force to an optimum value in correspondence to a friction coefficient between a wheel tire and a road surface while preventing the lock of a wheel. In antiskid control, a wheel cylinder pressure (W/C pressure) for causing the wheel braking force is selectively reduced, held, and increased in response to a slip state of the wheel.
An ABS actuator for carrying out ABS control is formed by integrally installing several control valves, several conduits, and an ABS reservoir in a housing. In the housing of the ABS actuator, non-return valves (check valves) for preventing reverse flow of brake fluid are also installed. For example, as described in JP-A-8-166073, a non-return valve is disposed in a conduit between a master cylinder and an ABS reservoir.
When the wheel cylinder pressure is reduced by ABS control, brake fluid is discharged from the wheel cylinder into the ABS reservoir. The brake fluid accumulated in the ABS reservoir is returned toward the master cylinder via a connduit connecting the ABS reservoir to the master cylinder by biasing force of a spring which biases a reservoir piston. However, when the master cylinder generates master cylinder pressure during a normal braking operation, it is necessary to prevent brake fluid from reversely flowing from the master cylinder into the ABS reservoir by the master cylinder pressure. For this purpose, a non-return valve is disposed in the conduit connecting the ABS reservoir to the master cylinder.
In detail, as described in the above-mentioned Patent Publication, the non-return valve is structured by a ball valve, a seat portion as a valve seat for the ball valve, a spring for biasing ball valve toward the seat portion, and a sleeve (plug) for supporting the spring, which are integrally assembled. The non-return valve is press-fit in the conduit to fix the non-return valve in the conduit.
However, because the above-described non-return valve is structured by different kinds of plural parts (ball valve, seat portion, spring and sleeve), and further these parts need to be assembled integrally, a manufacturing cost of the non-return valve is high.
In addition, before brake fluid is poured in a hydraulic path of a brake apparatus, the inside of the hydraulic path is evacuated to promote the pouring of brake fluid. However, in the conventional non-return valve, because the spring biases the ball valve toward the seat portion, a pressure for opening the ball valve is not zero (atmospheric pressure). For this reason, degree of vacuum in the hydraulic path cannot be risen.